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201.
Implicit and explicit integration in the solution of the absolute nodal coordinate differential/algebraic equations 总被引:1,自引:0,他引:1
This investigation is concerned with the use of an implicit integration method with adjustable numerical damping properties
in the simulation of flexible multibody systems. The flexible bodies in the system are modeled using the finite element absolute nodal coordinate formulation (ANCF), which can be used in the simulation of large deformations and rotations of flexible bodies. This formulation, when
used with the general continuum mechanics theory, leads to displacement modes, such as Poisson modes, that couple the cross section deformations, and bending and extension of structural elements such as beams. While these
modes can be significant in the case of large deformations, and they have no significant effect on the CPU time for very flexible
bodies; in the case of thin and stiff structures, the ANCF coupled deformation modes can be associated with very high frequencies that can be a source of numerical problems when explicit integration methods
are used. The implicit integration method used in this investigation is the Hilber–Hughes–Taylor method applied in the context of Index 3 differential-algebraic equations (HHT-I3). The results obtained using this integration method are compared with the results obtained using an explicit Adams-predictor-corrector method, which has no adjustable numerical damping. Numerical examples that include bodies with different degrees of flexibility
are solved in order to examine the performance of the HHT-I3 implicit integration method when the finite element absolute
nodal coordinate formulation is used. The results obtained in this study show that for very flexible structures there is no
significant difference in accuracy and CPU time between the solutions obtained using the implicit and explicit integrators.
As the stiffness increases, the effect of some ANCF coupled deformation modes becomes more significant, leading to a stiff
system of equations. The resulting high frequencies are filtered out when the HHT-I3 integrator is used due to its numerical
damping properties. The results of this study also show that the CPU time associated with the HHT-I3 integrator does not change
significantly when the stiffness of the bodies increases, while in the case of the explicit Adams method the CPU time increases
exponentially. The fundamental differences between the solution procedures used with the implicit and explicit integrations
are also discussed in this paper. 相似文献
202.
203.
以有限发射功率、迫零均衡为限定条件,利用现代凸优化理论和算法进一步进行多用户通信系统收发器的简化设计。将半正定规划模型等效转化为二阶锥规划模型。二阶锥规划模型将更加简单而且计算复杂度获得很大的改善。借助优化软件SeDuMi的计算机仿真表明:设计的收发器比现存收发 相似文献
204.
205.
206.
207.
208.
丁二烯气相聚合的负载型稀土催化剂研究 总被引:2,自引:1,他引:1
合成了负载型稀土催化剂,并将其用于丁二烯气相聚合.研究表明,硅胶负载Nd(naph)3-Al(i-Bu)3-Al(i-Bu)2Cl催化体系具有相当高的催化活性和立体定向性,其最佳组成:n(Al)/n(Nd)=40~60,n(Cl)/n(Nd)=3~7.添加适量单体丁二烯或异戊二烯,尤其是添加丁二烯,可成倍提高催化活性,随着聚合反应的进行,其速率在10min内迅速增加并达到峰值,随后降低,动力学行为属衰减型.所得聚丁二烯的分子量在几十万至百万,凝胶含量小于6%,顺-1,4结构含量达到98%左右. 相似文献
209.
CHEN Jing-Bo 《理论物理通讯》2004,41(4):561-566
The multisymplectic geometry for
the seismic wave equation is presented in this paper. The local
energy conservation law, the local momentum evolution equations, and
the multisymplectic form are derived directly from the
variational principle. Based on the covariant Legendre transform,
the multisymplectic Hamiltonian formulation is developed.
Multisymplectic discretization and numerical experiments are also
explored. 相似文献
210.
In this paper the analysis of structures with inelastic material behaviour is considered taking into account the evolution of defects and changes in mass density. The underlying kinematical concept of an oriented continuum is general enough to describe the micro- and macrobehaviour of material bodies appropriately. Based on the logical and consistent variational arguments for a Lagrangian functional the dynamic balance laws, boundary and transversality conditions, all related to the evolution of defect density and mass changes, are derived for macro- and microstresses of deformational as well as of configurational type. The adopted procedure, which formally leaves the balance laws unaltered, leads to the additional balance law for changes in defect density and additional boundary conditions for the changes in mass and defect densities. Driving forces or affinities, associated with the evolution of defect and mass densities, and a generalization of the J-integral representing the thermodynamic forces on defects are obtained. A nonlocal constitutive model accounting for changes in the defect density is presented. 相似文献